Nuts with direct torque screws over a tempered washer are well-known in the art, these nuts have direct torque screws over a tempered washer which are tightened through a torque wrench in order to make the summation of forces of each of the screws over the supporting base, thus stretching the stud of each screw and generating a tension therein.
Hytorc CLAMP nuts (Unex Corporation) are also known in the art, wherein a sleeve, a bush and a washer perform a similar function to that of stretching the screw stud, where a hydraulic torque wrench is required in order to obtain a preset pressure.
The hydraulic nuts available in the market often have the issue of exceeding the measure of stress of the nut body indicated by the manufacturer upon injecting the hydraulic fluid, and also the part that performs the function of pull knob, so the parts separate loosing the fluid and getting disabled.
U.S. Pat. No. 7,063,490, describes a hydraulic nut having a screw, which is movable in a fluid chamber of a nut body and which has a radial protrusion from the screw and a displacement bar mounted on the protrusion. The displacement bar overlies the nut body and extends past the nut body by an amount equal to the distance through which the hydraulic nut is to move a bearing assembly along a tapered shaft or move an adapter sleeve, or removal sleeve with bearing assembly on them.
U.S. Pat. No. 4,182,215, describes hydraulic prestressing nuts for setting a tensile stress in a bolt. The invention involves a nut body wherein an annular screw is arranged to be hydraulically extended from a bottom face thereof against a plate, head, platen, or the like, elevating the nut and extending the bolt therewith. A concentric loading ring is arranged with the nut body for turning into engagement with the place, such that when the loading ring is so extended, it provides a rigid columnar support to the annular piston. Tensile stress on the bolt is maintained by the loading ring. The nut of the present invention further involves a failsafe arrangement for providing a backup repressurization capability consisting of a second piston arrangement that can be independently pressurized at a primary seal failure, extending the primary piston therewith.